The only reason xbox360 is handedly outselling PS3 in the US is cross game chat. PS3 is outselling xbox360 everywhere else but still lag in global sales because xbox360 almost outsell PS3 2 to 1 in the US.
You could argue most of the 3rd party game are better on xbox 360, but I think this matters very little to majority of American video gamers (wal-mart shoppers, COD players, significant others gift shoppers, non-fanboys) and they don't even know which games perform better on which platform. All my friends on xbox live only get all games (especially) multiplayer on xbox live because party system is so difficult on PSN. Everything else (netflix app, bing, etc) doesn't factor much into buying a console.
If PS4 can even the playing field by inclusion of cross game chat/party, why pay to play online?
